There are many applications in which it is necessary to confirm the identity of an individual. Such applications include the purchase of merchandise using a credit card, cashing cheques at banks or validation of cheques when used in payment for merchandise or services, admission to locations where only authorised personnel must be allowed access, and the identification of users of a time-recording system for use in monitoring the arrival and departure of employees at a place of work.
In some of these applications it is necessary to ensure that the holder of such a card or any third party into whose hands it may pass as a result of theft or casual loss, is unable to change the code embodied in or on the card, and thereby gain unauthorised access or obtain merchandise dishonestly.
A number of methods have been described for ensuring that the codes cannot be altered without mutilating a card so drastically that it is no longer capable of being used. Among these methods are several in which the coding is concealed within the structure of the card, invisible to the naked eye but detectable by a variety of techniques depending on magnetic interaction, radio frequency coupling, radioactive detection, reflection or attenuation of infra-red radiation of other physical phenomena.
A number of techniques have been described in which infra-red radiation is applied to one side of a composite card and a series of infra-red detectors located on the other side respond to the presence or absence of a transmission path through the card at specified locations. Some such methods have been disclosed by Scuitto and Kramer in U.S. Pat. No. 3,875,375, by Lawrence Systems Inc., in U.S. Pat. No. 4,066,910, by Interflex Datensystem of Germany, in UK Pat. No. 2009477, by EMI Ltd, in UK Pat. No. 1581624 and by J. R. Scantlin of Transaction Technology Inc. in U.S. Pat. Nos. 3,858,032, 3,819,910 and 3,802,101.
Most of the above mentioned patents disclose techniques in which several parallel tracks of data are scanned by a set of several photodetectors, one such track being used as a clock track while the corresponding data bits in the other tracks are either translucent to represent a binary digit ONE or opaque to represent a binary digit ZERO or vice versa. The mechanisms used to transport the cards past the read heads and for effecting the parallel signal paths from the several tracks to the associated digital electronic systems have various levels of complexity according to the details of the intended application.